KR20090057262A - Nanocomposite particle and process of preparing the same - Google Patents

Abstract

A nanocomposite particle, its use as a catalyst, and a method of making it are disclosed. The nanocomposite particle comprises titanium dioxide nanoparticles, metal oxide nanoparticles, and a surface stabilizer. The metal oxide nanoparticles are formed hydrothermally in the presence of the titanium dioxide nanoparticles. The nanocomposite particle is an effective catalyst support, particularly for DeNOx catalyst applications.

Description

NANOCOMPOSITE PARTICLE AND PROCESS OF PREPARING THE SAME

The present invention relates to a nanocomposite particle and a method for producing the same. Nanocomposite particles are useful as catalysts and / or catalyst supports.

Titanium dioxide is widely used as a catalyst and / or catalyst support in many applications, including oxidation chemistry, hydrotreating, Claus reactions, photocatalysis, oxidization of volatile organic compounds and DeNOx reactions. For example, the use of titanium dioxide as a catalyst support for the selective catalytic reduction of NOx is described in US Pat. Nos. 4,958,586 and 5137855. Although any crystalline shape of titanium dioxide (anatase, rutile, alc brookite) is useful for catalysis, typically anatase may be preferred as described in US Pat. Nos. 5,309,353 and 6576589. .

Unfortunately, titanium dioxide is thermally unstable when used in high temperature environments such as DeNOx. At high temperatures, titanium dioxide nanoparticles tend to coalesce to reduce their surface area and porosity. Moreover, at high temperatures, anatase can be partially converted to rutile form.

Numerous countermeasures are used to solve the above-mentioned problems. One countermeasure is to add a second metal oxide. For example, US Pat. No. 5,139,322 discloses a dioxide support formed from the coprecipitation of a salt of titanium and zirconium to form a matured hydrosol to produce a dioxide support. U.S. Patent No. 50,139,22 discloses a process for making mixed oxides by cohydrolysis of an alkoxide mixture of titanium and alumina. U.S. Patent Publication No. 2003/0103889 describes a method for making a titanium dioxide-silicon composite prepared by combining a silica sol and titanium dioxide. When the second metal oxide is incorporated into the titanium dioxide lattice to form a homogeneous mixed oxide, the crystal lattice and catalytic properties of the titanium dioxide are affected.

Another approach to solving the thermal instability problem is to coat titanium dioxide. For example, U. S. Patent No. 5330953 discloses a configuration for forming a second coating on titanium dioxide particles comprising a first coating consisting of aluminum, silicon, zirconium, lanthanum and diphosphate coatings. In addition, US Pat. No. 5,921,92 discloses a method of coating titanium dioxide nanoparticles with a salt. The present invention uses a hydrothermal treatment process for precursor mixtures of titanium dioxide and sulfate to make titanium dioxide nanoparticles coated with sulfate in crystalline form. One problem with this method is that the coating can affect the catalytic properties of titanium dioxide.

Overall, new titanium dioxide nanocomposite particles and methods for their preparation are required. In particular, nanocomposite particles can improve thermal stability for catalyst applications.

The present invention relates to a nanocomposite particle and a method for producing the same. Nanocomposite particles include titanium dioxide nanoparticles, metal oxide nanoparticles, and surface stabilizers. Metal oxide nanoparticles are zirconium dioxide, cerium dioxide, hafnium oxide, tin oxide, niobium oxide and / or tantalum oxide. Surface stabilizers are silicon dioxide, aluminum oxide, phosphorous pentoxide, aluminum silicate and / or aluminum phosphate. Metal oxide nanoparticles are formed by hydrothermal treatment of an amorphous hydrated metal oxide in the presence of titanium dioxide nanoparticles.

The nanocomposite particles initially prepare a slurry comprising titanium dioxide nanoparticles, soluble metal oxide precursors and a solvent, and form a soluble metal oxide to form a slurry comprising titanium dioxide nanoparticles, amorphous hydrated metal oxide and a solvent. Precipitate the precursor. The slurry is hydrothermally treated to convert the amorphous hydrated metal oxide into metal oxide nanoparticles, producing nanocomposite particles comprising titanium oxide nanoparticles and metal oxide nanoparticles. Surface stabilizers are added before or just after hydrothermal treatment.

Amazingly, nanocomposites exhibit enhanced thermal stability and are effective catalyst supports for the DeNOx process.

Nanocomposite particles of the present invention include titanium dioxide nanoparticles, at least one metal oxide nanoparticles and a surface stabilizer.

The titanium dioxide nanoparticles of the present invention have an average crystal size of 200 nm or less, preferably 1 to 100 nm, more preferably 2 to 20 nm. Titanium dioxide nanoparticles can be brookite, anatase or rutile phase. However, it is preferable that the titanium dioxide nanoparticles predominate over anatase, as determined by the X-ray diffraction pattern. By the prevailing anatase, it means that the nanoparticles are preferably at least 95% anatase, more preferably at least 98% anatase. Generally, the specific surface area of the titanium dioxide nanoparticles is about 10-300 m ² / g, more preferably about 20-200 m ² / g.

Suitable titanium dioxide nanoparticles can be purchased from Millenium Chemicals (TIONA®G1) or Kerr McGee (Tronox®Hydrate Paste). In addition, titanium dioxide nanoparticles can be prepared by any process known in the art. Processes for producing titanium dioxide nanoparticles are well known in the art. For example, it is described in detail in US Patent No. 4012338.

Nanocomposite particles include at least one metal oxide nanoparticle. Metal oxide nanoparticles help to improve the thermal stability of the titanium dioxide nanoparticles. Suitable metal oxide nanoparticles have a low coefficient of thermal expansion, improved mechanical strength and thermal stability at elevated temperatures. The metal oxide nanoparticles of the present invention are zirconium dioxide, cerium dioxide, hafnuim oxide, tin oxide, niobium oxide, tantalum oxide and Nanoparticles of mixtures thereof. Preferred metal oxide nanoparticles are zirconium dioxide and cerium dioxide, most preferably zirconium dioxide nanoparticles. The metal oxide nanoparticles of the present invention have an average crystal size of 200 nm or less, preferably 1 to 50 nm, most preferably 2 to 10 nm.

In addition, the nanocomposite particles include a surface stabilizer. Surface stabilizers of the invention include silicon dioxide, aluminum oxide, phosphorus pentoxide, aluminum silicate and aluminum phosphate. More preferably, the surface stabilizer is silicon dioxide or aluminum oxide.

The nanocomposite particles preferably contain 50 to 95% by weight of titanium dioxide, 2 to 48% by weight of metal oxide, and 2 to 20% by weight of a surface stabilizer. More preferably, the nanocomposite particles comprise 60 to 90% by weight titanium dioxide, 4 to 40% by weight metal oxide and 4 to 15% by weight surface stabilizer.

The nanocomposite particles of the present invention show improved thermal stability. Preferably, the nanocomposite particles have a surface area of greater than 60 m ² / g after burning at 800 ° C. for 6 hours to form quicklime.

Metal Oxides of Nanocomposite Particles Nanoparticles are produced by hydrothermal treatment of amorphous hydrated metal oxides in the presence of titanium dioxide nanoparticles.

The process of preparing nanocomposite particles begins with the formation of a slurry comprising titanium dioxide nanoparticles, at least one soluble metal oxide precursor and a solvent. The order of adding the individual components to the slurry is not determined. For example, titanium dioxide nanoparticles may be initially added to the solvent followed by addition of at least one soluble metal oxide precursor. Optionally, a soluble metal oxide precursor is added to the solvent followed by the addition of titanium dioxide nanoparticles, or the metal oxide precursor and titanium dioxide nanoparticles are added to the solvent simultaneously, or the solvent can be added to the other two components. The slurry formed contains a metal oxide precursor and solid titanium dioxide nanoparticles dissolved in a solvent. Preferably, the slurry is homogeneous and will be mixed thoroughly to ensure that the metal oxide precursor is completely dissolved.

Preferably, the slurry comprises 3-30% by weight of titanium dioxide nanoparticles, more preferably 5-15% by weight, based on the total weight of the slurry.

The slurry comprises at least one metal oxide precursor of zirconium dioxide, cerium dioxide, hafnium oxide, tin oxide, niobium oxide or tantalum oxide, the metal oxide precursor (zirconium) forming a metal oxide when precipitated from a solvent , Cerium, aluminum, hafnium, tin and / or niobium). Although the process of the present invention is not limited by the choice of a particular metal oxide precursor, suitable metal components useful in the present invention include halide metals, metal oxyhalides, metal alkoxides of zirconium, cerium, hafnium, tin, niobium and tantalum. metal alkoxides, metal acetates, and acetyl acetonated metals, but are not limited thereto. For example, tetrachloride zirconium, oxitrichloride tantalum, acetic cerium acetate, acetylacetonate niobium and tetraethoxide tin can be used.

The solvent is any liquid capable of dissolving the metal oxide precursor. Preferably, the solvent is water. However, nonaqueous protic solvents with high dielectric constant or are suitable. The preferred non-aqueous protic solvent is an alcohol. Preferred alcohols include low aliphatic C ₁ -C ₄ alcohols such as methanol, ethanol, isopropanol, tert-butanol, and mixtures thereof. Mixtures of water and one or more non-aqueous protic solvents may also be used.

After the slurry is formed, the soluble metal oxide precursor is precipitated from the slurry to form an amorphous hydrated metal oxide. Any suitable method of precipitating amorphous hydrated metal oxide from solution may be used in the process of the present invention. For example, ion exchange, condensation reactions, and thermal hydrolysis techniques to form PH transfer, solvent transfer, insoluble salts or hydroxides can be used. Preferably, the pH of the slurry is adjusted from PH7 to PH10 by adding an acid or base capable of precipitating metal oxides from the slurry. PH modulators are bases or acids that degrade during post-treatment by calcination of the nanocomposite particles. Suitable bases include amines having _a pK _a of 9.0 or more, ammonia and any organic base. Most preferred is ammonia. In addition, any inorganic or organic acid may be used. Preferred acids include nitric acid sand, sulfuric acid and hydrochloric acid. Nitric acid is most preferred.

After precipitation, the slurry contains titanium dioxide nanoparticles, amorphous hydrated metal oxide and a solvent. Amorphous hydrated metal oxide may precipitate on the surface of titanium dioxide nanoparticles, free-floating in a slurry or a mixture of both.

After the precipitation step, the slurry is hydrothermally treated to convert the amorphous hydrated metal oxide to metal oxide nanoparticles, and to produce the titanium oxide nanoparticles and the metal oxide nanoparticles to nanocomposite particles. Hydrothermal treatment is the heating of a slurry at high temperatures, preferably at high pressures. Preferably, the slurry is heated at a temperature of 60 ° C.-250 ° C. and 20-500 psig pressure. More preferably, the slurry is heated at a temperature of 80 ° C-130 ° C and a pressure of 20-200 psig.

Preferably, the slurry is hydrothermally treated at a time period of 3 to 24 hours, but the time is not determined. Temperature, pressure and hydrothermal treatment time should be sufficient for nucleation and growth of metal oxide nanoparticles. One advantage of hydrothermal treatment is the formation of metal oxide nanoparticles under relatively mild reaction conditions that minimize any influence on the surface properties and crystal structure of the titanium dioxide nanoparticles.

Surface stabilizers are added before or immediately after hydrothermal treatment. In one embodiment, the surface stabilizer may be added to the slurry at any point prior to hydrothermal treatment. For example, the surface stabilizer may be added to the slurry prior to precipitating the amorphous hydrated metal oxide or after precipitating the amorphous hydrated metal oxide. The slurry can be prepared by the method described above. Optionally, the surface stabilizer can be added immediately after hydrothermal treatment. That is, prior to separation of the nanocomposite product from the solvent or prior to the selective calcination process. Preferably, the surface stabilizer may be added after thoroughly mixing the slurry. Generally, the slurry is mixed for 1 minute to 3 hours before the surface stabilizer is added. Suitable components of the surface stabilizer include silicon dioxide colloids, halogenated or alkoxides silicon and amorphous silicon dioxide including aluminum and aluminum phosphate.

After hydrothermal treatment, the nanocomposite product is preferably separated from the solvent by any means (eg, filter, decantation, centrifugation, etc.), washed with water and dried. Preferably, the nanocomposite particles are calcined by heating at elevated temperatures. Calcination can be carried out in the presence of oxygen-free inert gas or oxygen (eg air) such as nitrogen, argon, neon, helium or mixtures thereof. Alternatively, the calcination can be carried out in the presence of a reducing gas such as carbon monoxide. Calcination is preferably carried out at a temperature of at least 250 ° C. More preferably, the calcining treatment temperature is preferably 300 ° C to 1000 ° C. Generally, a calcination time of about 30 minutes to 24 hours will be sufficient.

The present invention includes a catalyst comprising nanocomposite particles. The catalyst comprises nanocomposite particles and at least one metal component. Metallic components include one or more metals including platinum, gold, silver, palladium, copper, tungsten, molybdenum, vanadium, iron, rhodium, nickel, manganese, chromium, carbide and ruthenium. The metal component may be the metal itself or any compound comprising the metal. Preferably, the metal component is a metal oxide.

In general, the amount of metal present in the catalyst will be in the range of 0.001-30% by weight, preferably 0.005-20% by weight, in particular 0.01-10% by weight, based on the total weight of the catalyst.

The catalyst can be prepared by any suitable method. In one embodiment, the metal component is added during the preparation of the nanocomposite particles themselves. For example, the metal component may be added to the slurry before or after the hydrothermal treatment and treated in the same manner as described above. Optionally, the metal component can be deposited directly on the nanocomposite particles. For example, the metal component may be supported by saturation, adsorption, precipitation, and the like. Suitable metal components include metal alkoxides such as tungsten ethoxide, metal halides such as tungsten chloride, metal oxyhalides such as tungsten oxychloride, metallic acids such as tungstic acid, tungsten ammonium, vanadium pentoxide, molybten oxide, cooper monoxide In addition to the same metal oxide, the metal itself is included.

Preferred catalysts include tungsten trioxide and / or vanadium pentoxide. Preferably, the catalyst is 0.1 to 10% by weight vanadium pentoxide and 4 to 20% by weight tungsten trioxide, more preferably 0.2 to 7% by weight vanadium pentoxide and 4 to 16% by weight tungsten trioxide, more preferably 0.2 to vanadium pentoxide 5% by weight and 5-12% by weight of tungsten trioxide.

Nanocomposite particles may be calcined before or after addition of the metal component. The temperature at which the nanocomposite particles are calcined depends on the end use for which they are intended. Preferably, the calcination is carried out at a temperature of 400 ° C to 900 ° C, more preferably at 650 ° C to 750 ° C.

Catalysts are particularly useful in DeNOx applications. DeNOx applications include contacting a waste stream containing nitric oxide with a catalyst to reduce the amount of nitric oxide in the waste stream. Such applications are well known in the art. In this process, the nitrogen oxides are reduced by ammonia (or other reducing agent such as unburned hydrocarbons present in the waste gas) in the presence of a catalyst with nitrogen. For example, U.S. Patent Nos. 3279884 and 4085193 describe the above-described actions in detail.

The examples to be described below merely illustrate the invention. Those skilled in the art will recognize other modifications that fall within the scope of the claims and the spirit of the invention.

Example 1: Nanocomposite Preparation

Nanocomposite 1A

Preparation of Titanium Dioxide Nanoparticles: TiSO ₄ solution (2000 g, 7.6 wt% TiO ₂ ) is injected into a 3-L reactor and the pH of the solvent is ammonium hydroxide solvent (29% NH ₃ in water, allrich (Aldrich) and adjust to about 1. Urea 550g is dissolved in solution and the temperature rises to 98 ° C. for 3 hours. After cooling, the titanium dioxide nanoparticles are separated by a filter and washed with water. The filtered titanium nanoparticles are dispersed again in water to form a 2-L slurry.

Nanocomposite Preparation: Half of the 2-L slurry is placed in a 2-L beaker and Zr0Cl ₂ · 8H ₂ O (50 g) is dissolved in the slurry. Under vigorous stirring, the ammonium hydroxide solvent (29% NH ₃ in water) is added slowly until the slurry has a pH of about 10 and ZrO ₂ precipitates. And Fumed SiO ₂ (5 g) is added to the slurry, and the slurry is placed in a 2-L stirred hydrothermal reactor and hydrothermally treated at 90 ° C. for 12 hours. The output is cooled, filtered by a filter and washed with water. The washed mass is dried in an oven at 100 ° C. for 12 hours and calcined in a furnace at 800 ° C. for 6 hours to produce nanocomposite 1A.

Nabo composite material 1B-1H : The nanocomposite particle manufacturing process of the nanocomposite material 1A described above is performed in the same manner except that commercial TiO ₂ nanoparticles are used. Particles 1B, 1C, and 1D, 1E, and 1F use SiO ₂ fumigation as the surface stabilizer, particle 1G uses SiO ₂ sol as the surface stabilizer, and particle 1H uses aluminum phosphate as the surface stabilizer. The amount of TiO ₂ ZrO ₂ and surface stabilizer is varied to provide nanocomposites 1B, 1C, 1D, 1E, 1F, 1G of the variable composite.

Comparative nanocomposite material 1I-1J : The process for preparing nanocomposite particles of nanocomposite material 1B is omitted except for the use of ZrO _divalent nanocomposite 1I, and the use of SiO ₂ for nanocomposite 1J is omitted. The same goes for.

The final nanocomposite (which is then hydrotreated at 800 ° C.) is analyzed for component, surface area, pore volume and TiO 2 and ZrO 2 crystal size measurements.

Formation of metal oxide nanoparticles following hydrothermal treatment was confirmed by X-ray diffraction testing. Prior to hydrothermal treatment, titanium dioxide nanoparticles were detected by X-ray diffraction, and in the subsequent hydrothermal treatment, the second crystalline phase was detected corresponding to the metal oxide nanoparticles.

Example 2: DeNOx Catalyst Preparation

The catalyst is prepared according to the procedure disclosed in US Pat. No. 10/968706. The nanocomposite (75 g) is slurried in deionized water (175 mL) and concentrated sulfuric acid is added until the pH is zero. Ammonium paratungstate solution (9.38 g AMT in 150 mL deionized water produced by mixing at 50 ° C.) is added to the nanocomposite slurry and stirred for 1 hour. The powder is filtered, dried at 110 ° C. and calcined at 500 ° C. for 6 hours. The powder (10 g) is added to 0.185 g MEA (monoethanolamine) and 0.092 g V ₂ O ₅ ) in 20 mL of deionized water formed by stirring at 60 ° C. until dissolved, and stirred for 10 minutes. The solvent is evaporated in vacuo and the solid is dried at 110 ° C. and calcined at 600 ° C. for 6 hours. The catalyst comprises approximately 10 wt% WO ₃ and 0.9 wt% V ₂ O ₅ .

Nanocomposites 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H, 1I, 1J are used to form catalysts 2A 2B, 2C, 2D, 2E, 2F, 2G, 2H, 2I, 2J.

Example 3: DeNOx Test

The catalyst is placed in a conventional plug flow reactor with components consisting of 300 ppm NO, 360 ppm NH3, 3% O2, 10% H2O and balanced N2 with a space velocity of 80000 / hr. NH3 catalytic reduction is performed at 270 ° C and 320 ° C.

The results are shown in Table 2. The results are recorded as NO Conversion and Activity. Activity is expressed as k ^* tau and tau k ^* denotes a multiplication of processing activity by a constant contact time. The ammonia selective catalytic reduction is first order with respect to NO and zero order with respect to NH ₃ , and the activity is calculated as k ^* tau = -ln (1-conversion) in the degree of conversion, where the degree of conversion is expressed as a few minutes.

Table 1: Amount of TiO ₂ , ZrO ₂ and Surface Stabilizers in Nanocomposite Particles

                                  Table 2: DeNOx Results

Claims (20)

(a) titanium dioxide nanoparticles; (b) metal oxide nanoparticles selected from the group consisting of zirconium dioxide, cerium dioxide, hafnium oxide, tin oxide, niobium oxide and tantalum oxide; And (c) a surface stabilizer selected from the group consisting of silicon dioxide, aluminum oxide, phosphorus pentoxide, aluminum silicate and aluminum phosphate, The metal oxide nanoparticles are nanocomposite particles formed by hydrothermal treatment of an amorphous hydrated metal oxide in the presence of the titanium dioxide nanoparticles. The method of claim 1, The titanium dioxide nanoparticles are nanocomposite particles, which are mostly anatase, The method of claim 1, The metal oxide nanoparticles are zirconium dioxide nanocomposite particles. The method of claim 1, A nanocomposite particle comprising 50-95 wt% titanium dioxide nanoparticles, 2-48 wt% metal oxide nanoparticles, and 2-20 wt% surface stabilizer. The method of claim 1, Nanocomposite particles having a surface area of 60 m ² / g or more after calcination at 800 ° C. for 6 hours. The nanocomposite of claim 1 and at least one metal component comprising a metal selected from the group consisting of platinum, gold, silver, palladium, copper, tungsten, molybdenum, vanadium, iron, rhodium, nickel, manganese, chromium, cobalt and ruthenium Catalyst comprising a. The method of claim 6, Said metal component is selected from the group consisting of tungsten trioxide and vanadium pentoxide. The method of claim 7, wherein The vanadium pentoxide is 0.1 to 10wt%, the tungsten trioxide is a catalyst containing 4 to 20wt%. A method comprising contacting the catalyst of claim 7 to a waste stream comprising nitric oxide to reduce the amount of nitric oxide in the waste stream. (a) forming a slurry comprising titanium dioxide nanoparticles, at least one soluble metal oxide precursor and a solvent; (b) precipitating the soluble metal oxide precursor to form a slurry comprising titanium dioxide nanoparticles, amorphous hydrated metal oxide and a solvent; (c) hydrothermally treating the slurry of step (b) to convert the amorphous hydrated metal oxide into metal oxide nanoparticles; And (d) optionally, calcining the nanocomposite particles; Surface stabilizer is a method for producing nanocomposite particles added before or immediately after hydrothermal treatment. The method of claim 10, The hydrothermal treatment is a method for producing nanocomposite particles carried out at a temperature of 60 ~ 250 ℃, pressure 20 ~ 500 psig. The method of claim 10, The titanium dioxide nanoparticles are mostly anatase method for producing nanocomposite particles. The method of claim 10, The soluble metal oxide precursor is selected from the group consisting of zirconium, cerium, aluminum, hafnium, tin and nionium. The method of claim 10, The surface stabilizer is selected from the group consisting of amorphous silicon dioxide, halides or alkoxides of silicon and aluminum and aluminum phosphate. The method of claim 10, The nanocomposite particles are 50 to 95wt% of titanium dioxide nanoparticles, 2 to 48wt% metal oxide nanoparticles and 2 to 20wt% surface stabilizer. The method of claim 10, Adding at least one metal component comprising a metal selected from the group consisting of platinum, gold, silver, palladium, tungsten, vanadium, molybdenum and copper. The method of claim 16, And said metal component is selected from the group consisting of aluminum paratungstate and vanadium pentoxide. The method of claim 17, The nanocomposite particles are 0.1 to 10wt% vanadium pentoxide and 4-20wt% of tungsten trioxide. The method of claim 10, The nanocomposite particles are calcined at 800 ° C. for 6 hours and then have a surface area of 60 m ² / g or more. The method of claim 10, The solvent is a method for producing nanocomposite particles of water.